The present invention relates to an improved device for providing speed instruction signals for an elevator.
A speed feedback control system has previously been employed in which the speed of the cage of an elevator is controlled according to deceleration instruction signals so that the cage is decelerated and stopped at desired floors without exerting uncomfortably high acceleration or deceleration forces. Recently, a method has been proposed in which the speed feedback control system is effected with an electronic computer.
In the conventional method, as described in detail later, a cage position signal is detected by counting the number of pulses corresponding to the distance through which the cage has moved. When the cage reaches a position a predetermined distance before a floor where the cage is to be stopped, by counting pulses, the remaining distance between the position and the desired floor is successively calculated and a deceleration instruction value corresponding to the remaining distance thus calculated is read out as a deceleration instruction signal. The cage is decelerated in accordance with this signal until it stops at the desired floor.
If the maximum rated speed of the cage of the elevator is 90 m/min or higher, sometimes it is impossible to run the cage at the maximum rated speed during a period of running the cage because it is strongly required that a person in the cage not be made uncomfortable. Accordingly, in this case, it is necessary that the cage run at a speed (hereinafter referred to as "a partial speed" when applicable) lower than the rated speed. In general, whether or not the cage should be run at the rated speed is determined according to the number of floors, that is, the distance between floors, and the highest speed during a run is also determined according the number of floors. For instance with a maximum rated speed of 90 m/min, the partial speed may be employed for single-floor operation and the rated speed employed for operations other than single-floor operation. With a rated speed of 105 m/min, the partial speed may be employed for single-floor operation and two-floor operation, and the rated speed employed for three-floor operation amd more-than-three-floor operation. The term "single-floor operation" is intended to mean that the cage is moved between two adjacent floors, for instance, from the first floor to the second floor. The term "two-floor operation" is intended to mean that the cage is moved, for instance, from the first floor to the third floor. The same concept is applicable to the term "three-floor operation", etc.
Depending on the construction of a building, the distances between the floors may not be uniform. Therefore, if the distance between adjacent floors is sufficiently long, the maximum rated speed may be employed for single-floor operation. However, in the conventional system, for such a short floor distance the cage is run at the partial speed and accordingly the transportation efficiency is unavoidably low. Especially in an AC elevator using an induction motor as its hoisting motor, running the cage at a low speed increases power consumption with the motor generating much heat. This operation is uneconomical. That is, running an AC elevator at the maximum rated speed provides the highest efficiency. If, in an elevator employing DC braking or opposite phase braking for decelerating the cage, DC braking or opposite phase braking is applied to the cage while it is moving downwardly with a full load, the heat generation and power consumption of the motor are increased. Therefore, it is necessary to apply the full voltage to the motor and to apply regenerative braking to the motor during deceleration. Thus, it is very important to determine whether or not the cage can be run at the rated speed.
Accordingly, an object of the invention is to provide an elevator control device in which the above-described difficulties have eliminated. More specifically, it is an object of the invention to provide such an elevator control device in which it can be readily determined whether or not the cage can be run at the maximum rated speed and in which operational modes corresponding to high transportation efficiency can be selectively employed.